This project continues to develop effective therapies for patients with aplastic anemia who are not candidates for genotypically HLA-identical donor bone marrow transplants. Previous studies performed in Seattle have shown that immunosuppressive regimens including anti-human thymocyte globulin (ATG), high or low-dose corticosteroids and androgens, achieves long-term survival in 44% of patients. In an effort to improve these results the role of hematopoietic growth factors given singly or in combination along with immunosuppressive therapy will be evaluated. Long-term follow-up of patients will determine the incidence of late complications such as recurrent aplasia, myelodysplastic syndrome, and paroxysmal nocturnal hemoglobinuria (PNH). Statistical analyses will be used to (1) identify clinical or laboratory parameters associated with response to therapy and (2) compare the results of immunosuppressive therapy to those of marrow transplantation.